The overall significance of this project relates to the ability to imbalance the DNA base excision repair (BER) pathway in ovarian tumor ceils, increasing their sensitivity to chemotherapeutic and ionizing radiation (IR) agents. We will attempt to accomplish this goal using mutants of the human apurinic/apyrimidinic endonuclease (APE1) enzyme, overexpression of N-methylpurine DNA glycosylase (MPG), both targeted to the nucleus and mitochondria, as well as small (short) interfering RNA (siRNA) for APE1. We will also utilize folic acid-derivatized liposomes and adenoviral targeting along with tumor specific promoter expression using the human telomerase reverste transcriptase (hTERT) promoter in both cell lines and an NOD/SCID animal model to develop the usefulness of this approach. Hypothesis: Overexpression of MPG in the nucleus and/or mitochondrial compartments, altered human APE1 proteins (dominant-negative), or siRNA for APE1 either independently, or in various combinations will enhance ovarian cancer cells to standard or decreased levels of commonly used chemotherapeutic agents (e.g. alkylators) and/or IR. The Specific Aims are: Specific Aim 1: This first aim includes determining the effectiveness of overexpressing MPG or dominant-negative APE1 in multiple ovarian cancer lines and evaluating tumor cell response to chemotherapeutic and IR treatment. This includes both nuclear and mitochondrial targeting of the MPG enzyme and overexpression and the knockdown of APE1 with siRNA. Specific Aim 2: Determine the effects of co-overexpression of nucMPG, mitoMPG and nuclMPG+mitoMPG, nucMPG+APE1 mutant, mitoMPG+APE1 mutant and nucMPG or mitoMPG and APEI-siRNA. We will monitor whether combined expression enhances the tumor cell killing effect of chemotherapeutic agents or IR. Specific Aim 3: Constructs using the hTERT promoter will be used in ovarian cancer cell lines in both plasmid (folic acid-derivatized liposome) and adenoviral based delivery systems for tumor specific expression studies using best candidate APE1 mutants, nuc- or mitoMPG, or siRNA as determined by the results in Aims 1-2. Specific Aim 4: Determine in vivo chemo- and radiosensitivity due to the expression of the various constructs of APE1 mutants, or nuc-/mitoMPG as well as APEI-siRNA in NOD/SCID mice. Adenoviral constructs with the hTERT promoter as well as folic acid-derivatized liposomes containing selected genes from the first three aims will be used with xenograft NOD/SCID mice. If successful, we feel these studies will create very effective reagents in a therapeutic gene transfer/therapy setting in the clinic, as well as shed light on the role of both nuclear and mitochondrial BER in cancer cells.